The present invention is directed to an automatic tool changer primarily intended for use with workpiece handling apparatus employed to transfer sheet metal panels from one work station to the next in a production line where the line is changed over from time to time from producing panels of one configuration to producing panels of a different configuration.
Sheet metal automobile body panels are typically formed by passing the sheet metal blank through a series of stamping dies which progressively transform the original flat rectangular sheet metal blank into the desired final panel configuration. The presses in which the dies are mounted are massive machines. The capital investment required to set up a single stamping production line is such that the line cannot be dedicated to the production of only a single type of panel. Conversion of the line from the production of one type of body panel to another requires not only the changing of the dies in the various presses, but also will require, for reasons to be explained below, changes to panel gripping and handling devices employed to transfer the panels from one press to the next.
In the past, the standard practice was to operate the line on relatively long production runs--that is to produce a relatively large number of panels of one type before changing the line over to produce panels of a different type. This procedure required a substantial amount of storage space to store the panels. A production run on the stamping line might, for example, produce enough panels to supply the assembly line for ten days. The rate at which the panels could be produced by the stamping line was substantially higher than the rate at which the panels were required at the assembly line, hence the time constraints on changing the line over from one panel to another were quite generous.
At present, however, the preferred procedure is the so-called "just in time" production system in which the storing of large numbers of panels in inventory is substantially eliminated. Practice of the "just in time" procedure dictates relatively short production runs with rapid changeover of the stamping line from one panel to another being required.
As noted above, the changeover of the stamping line from the production of one type of panel to the production of a different panel requires not only the changing of the dies in the presses, but also almost invariably requires the changing of the panel engaging elements of the article handling system employed to transfer the panels from one press to the next.
Typically, the panels are moved into and out of the presses by a group of vacuum cups mounted upon a frame to grip the upper surface of a generally horizontally disposed panel to stably support the panel so that it can be lifted by the frame from one location, transported horizontally and then lowered and released at another location. Because the size and configuration of the panels can vary considerably from one type of panel to another, the number and location of the vacuum cups on their carrying frame must be conformed to the shape of the particular panel which is to be handled. Typically, the distance between adjacent presses is such that a handling device employed to manipulate the vacuum cup carrying frame to extract a panel from one press cannot conveniently be employed to load the extracted panel into the next press. The most common arrangement finds a vacuum cup carrying frame being manipulated by a take-out device to extract the panel from the first press and to load the panel upon a panel receiving "nest" on a transfer conveyor which then conveys the panel to a location adjacent the next press where a second vacuum cup carrying frame is manipulated by a loading device to remove the panel from the transfer conveyor nest and load it into the second press.
In this system, three panel supporting devices are required--two vacuum cup carrying frames, one for each of the take-out and loading devices, and a third panel supporting device or nest for supporting the panel upon the transfer conveyor.
The present invention is especially directed to systems which enable a rapid and largely automated change of the panel engaging devices of such a transfer system.